1. Field of the Invention
This invention relates generally to a biopsy instrument; viz., a device for removing a sample of tissue from a human being or an animal. More particularly, the invention relates to an automated biopsy instrument in which a spring-loaded outer cannula is driven over an inner stationary stylet to obtain the tissue sample.
2. Description of the Related Art
The procedure known as biopsy, or the removal of samples of human and animal internal tissue, has been for many years a favored method for the nonsurgical diagnosis of tissue. Traditionally, biopsy has been performed in a two-step manual technique employing a needle in which an outer hollow cutting cannula telescopically receives an inner stylet which is slidable between retracted and extended positions relative to the cannula. In performing the first step of the technique, the physician places the tip of the needle (with the stylet retracted inside the cannula) against the tissue mass to be sampled and manually drives the stylet forward into the tissue mass. In a typical instrument of this type, the stylet extends rearwardly therefrom and is fitted with a push-knob to facilitate the driving of the stylet in the forward direction. To carry out the second step, the physician manually drives the cutting cannula forwardly over the stylet, thereby severing a tissue sample and retaining it within the cannula's hollow interior.
Examples of manually operated biopsy needles of this general type are disclosed in U.S. Pat. No. 4,600,014, issued July 15, 1986 to D. Beraha for "Transrectal Prostate Biopsy Device and Method", and U.S. Pat. No. 3,477,423, issued Nov. 11, 1969 to L. K. Griffith for "Biopsy Instrument".
Such manually operated two-step devices are awkward to manipulate, and the tissue samples obtained may often be unsatisfactory. The depths to which the stylet and the cannula are driven into the tissue mass must be carefully controlled for accuracy and efficiency. Caution is required, as well, in applying the force with which the stylet and cannula are plunged forward. Too little force may not sever the tissue sample from the mass; too much force may cause unnecessary damage to the surrounding vital tissues.
In an effort to remedy these problems, various automated devices have been developed. For example, U.S. Pat. No. 3,452,741, issued July 1, 1969 to R. C. Schaffer for "Conetome", discloses an instrument for performing cervical biopsies in which an electric motor imparts reciprocating movement to a pair of serrated scalpel blades.
U.S. Pat. No. 4,667,684, issued May 26, 1987 to H. G. Leigh for "Biopsy Device", discloses a movable stylet telescopically received in a hollow movable cannula, both the stylet and the cannula being mounted to hubs within a pistol-style grip. In use, the stylet is first manually advanced into the tissue and the cannula is then driven over the stylet by depressing a trigger.
U.S. Pat. No. 4,699,154, issued Oct. 13, 1987 to one Lindgren for "Tissue Sampling Device", discloses a complicated biasing mechanism in which a release button is depressed to cause a spring-loaded stylet to be advanced into the tissue mass. The forward movement of the stylet also triggers the delayed release of a spring-loaded outer cannula, which slides over the stylet to sever the tissue sample.
The aforementioned U.S. Pat. No. 4,600,014 to Beraha discloses an embodiment in which, after a slidable stylet is manually advanced into the tissue mass, a spring-loaded outer cannula is released and driven over the stylet to sever the tissue sample.
Several prior automated biopsy instruments employ a stylet formed with an elongated transverse slot or notch adjacent to its sharpened tip. This slot provides a pocket in which is captured a severed tissue sample when the cannula is driven forward over the stylet in the second step of the biopsy procedure. Typical of this form of stylet is the TRU-CUT.RTM. Needle marketed by Travenol Laboratories, Inc., Deerfield, Ill.
An important feature of another known device, The Roth Biopsy Needle, marketed by Cook Urological, Inc., Spencer, Ind., is a stylet which is manually adjustable between extended and retracted positions for reasons which will be apparent from the following description of its various methods of operation. The stylet is loaded from the rear of the instrument and extends behind the instrument at all times. The stylet is mounted to a U-shaped handle which is engageable with the body of the instrument in two positions corresponding to the extended and retracted stylet positions. A spring-loaded cannula is also movable between a charged or rear position and a discharged or advanced position.
In one method of using the Roth needle, the physician first adjusts the stylet manually to its retracted position and moves the cannula manually to the charged position to expose the sharpened tip of the stylet. He then penetrates the tissue mass with the stylet and depresses a button-release to cause the cannula to be driven by the spring forwardly over the tip of the stylet to sever the tissue sample and retain it within the hollow tip of the cannula. It is to be borne in mind that the stylet of the Roth needle is movable, as mentioned above, and that the button-release is exposed at all times and therefore subject to inadvertent actuation. It should also be noted that because the stylet and the associated U-shaped handle extend behind the instrument, the stylet and handle are always exposed and are therefore vulnerable to accidental impact or unintended forces, thereby creating a risk that the stylet may be inadvertently advanced into the body of the patient with possibly deleterious consequences.
In another method of using the Roth needle, the physician proceeds as before, but after penetrating the tissue mass he manually advances the stylet to its extended position to expose the transverse slot or gap therein described above. When the cannula is advanced, the tissue sample is severed and captured in the pocket formed by the slot.
In an alternative variation of the foregoing method, the physician may begin the procedure with the stylet in the extended position and the cannula in the discharged mode. Once the tissue has been penetrated, the cannula is manually retracted to expose the transverse slot. However, it is to be noted that all stylets formed with such a tissue pocket, whether employed in the Roth needle or in other biopsy instruments, become unstable when tooled to gauge sizes larger than 20 gauge (i.e., 21, 25 gauge). At higher gauge numbers (i.e., smaller diameter stylets) the bridge joining the stylet's proximal and distal ends at the tissue pocket becomes increasingly flexible, and therefore the stylet becomes physically unstable and its direction impossible to control with any precision when the slot or gap is exposed during penetration of the tissue mass by the stylet. Moreover, certain areas of the body such as the pancreas, thyroid, and nonpleural-based intrapulmonary lesions are routinely biopsied with needles smaller than 20 gauge (i.e., 21 gauge) to reduce the incidence of hemorrhage and pneumothorax.
In any event, the various automated biopsy instruments presently known tend to be heavy, difficult to manipulate, and incorporate biasing mechanisms which are either complicated in construction or require undue force to operate. Such limitations diminish the physician's control over the instrument and the precision with which biopsies may be performed. These instruments may be subject to inadvertent movement or torque which may, in turn, subject the patient to unnecessary trauma and risk. This is especially true of instruments which permit or require adjustment of the relative positions of any of their elements before the cannula is moved forward to sever the tissue sample. Similarly, the length of time required to perform a biopsy increases as the physician's degree of control of the instrument decreases, further elevating the risk to which the patient may be exposed. Finally, both physician and patient are exposed to the risk of inadvertent advancement of the cannula when the instrument is in its charged condition.